I try to save vector or default list on storage. All work fine until i close the application and open again. When i call to Storage , the storage don't find this vector.
Do have Problem to use this objects with Storage in lwuit?
The writeObject method accepts a second parameter as a Object. It returns true or false. If you object is suitable in the Storage you will get true. Try to put this vector and see what returns this method.
Last week I try to put a custom object and it doesn't work. I think hashtables can be in Storage, but ListModels doesn't.
Storage API
Related
If I have an existing image, how can get a reference to its Image::Info object? In particular, I want to read an option (that was previously set using image.define(...)) from it using the [] operator.
If there is any other way to read a value set via image.define(...) from an image, that would be perfect as well.
The define method is the same as []=, so you can get the option value using [].
I have iOS app that takes data from the server as json and then serializes them into objects of different types. Types can be complicated, can contain subtypes, can inherit, so there is no any limitations. Another thing that makes everything even more complicated is some of types are stored as AnyObject? and only in run time they are being serialized into real types accordingly to the specific rules. Something like that:
class A {
var typeName: String?
var b: AnyObject?
}
Then when it's serialized it can be done something like that:
if let someClass = NSClassFromString(typeName) as? SomeGenericType.Type{
b = someClass.init()
}
Also querying should be done on all the data. Currently I'm trying to store all of them locally, then load into memory and query there from the code. I'm using User defaults, but they have some limitations, also I needed to provide custom coding to make it work, and each time when I add a new field it turned out that I missed something in coding and nothing works. So it's pain.
Ideally I would just do some magic command and all the objects are sent to local storage no matter how complicated they are. The same to extract them from this storage. Also, user change data so I can't just store primary Json. And I don't want to covert objects back to Jason as for it's pain too.
Any suggestions?
If you want to use sqlite then You can store whole object in one row! I means you can create table with 2 columns one is id and second is your dataobject(it's data type should be blob). Then convert your whole object into data. Then store in sqlite table and retrieve it as data then convert it to object when want to use. By this way your object will remains in same format as you asked
Firebase while meant for online synching and storage can also cache everything locally in case you are offline and perform query's against the local cache. It uses JSON.
CouchDB also has a mobile version for iOS.
Both of those are over kill if your dataset is small; you can just store it as a text file and read the JSON back in. See performance characteristics here. The graph is for a 7MB file so if you are significantly less than that your load time may be minimal.
NSKeyedArchiver.archivedData(withRootObject:) is great for storing custom objects as Data objects. The only thing you need to do to be able to use this is to make your custom objects conform to NSCoding. A great example can be found here:
Save custom objects into NSUserDefaults
Once you have the Data version of the object, it can easily be stored in UserDefaults, as a property in CoreData, or even in the app's keychain entries. Depending on your use case, sensitivity of data, and how much data you intend to store, you might want to use any number of storage methods. NSKeyedArchiver.archivedData(withRootObject:) allows you to pretty much use any of them.
I have a very simple question, I just can't find a proper answer. That's
[NSKeyedArchiver archiveRootObject:value toFile:filePath];
according to apple documentation here, the above function:
Archives an object graph rooted at a given object by encoding it into
a data object then atomically writes the resulting data object to a
file at a given path, and returns a Boolean value that indicates
whether the operation was successful.
My question is, if I call this function multiple times with same file path, does it overwrite the previous value in this file? and Can I write empty array to the file by using this function?
Yes, it will overwrite the previous value, and yes you can write an empty array to the file by using that function.
The implementation of that method doesn't care about what's there, it will overwrite whatever it is.
I have a database object and some photos objects.
The database object contains an integer property and a mutable dictionary property.
The integer keeps track of the next free number to use as a mutable dictionary key when I create a new photo object and the mutable dictionary contains pointers to photo objects.
Photo objects contain an image, an image description and the date the image was taken.
I've been using NSKeyedUnarchiver and NSKeyedArchiver to read and write these objects in and out when my applicationDidBecomeActive and applicationWillResignActive methods trigger.
And, it's all been working well. When applicationWillResignActive triggers, it calls NSKeyedArchiver and points it to the database object as the root. The coder then writes out the integer and then when it encounters the mutable dictionary, it descends into it and each photo object is called to save its properties which are the image, the description and the date.
As I said, it's all been working well. But, it has seemed slower and slower as the number of photos has increased so I did some timings.
I found that reading the archive in is roughly 25 times faster than writing it out.
So, I conceived the idea of only writing out the photos which are new or changed as a method of speeding up the write side. After all, most of the photos are from past sessions and I might have 30 or 50 of them from before and I might only shoot two or three new ones this time.
I created some flags that indicate if a photo is new or old. When applicationWillResignActive triggers and I find myself down in the photos object handling each encodeWithCoder call, I save the image, description and date if the photo is new and I skip saving if it is old.
Well, I did not get the result I'd hoped for :-)
When applicationWillResignActive triggers, all the photos I skip writing out end up getting written out as empty photo objects which overwrites the previous photo objects out there with the same key. Then, when I load them back in, I've got bupkis, nada, zip.
First question, I guess, is can I write out only part of my object tree and have the parts I don't write out still remain out there intact from an earlier full write? I'm beginning to wonder if that might be a naive idea.
Gallymon
Using archives of some array of objects is going to be increasingly inefficient as the archive grows. This is exacerbated by the fact that your objects include images. Two thoughts:
You should consider using Core Data for storing this data. (You could use SQLite, directly, too, but Core Data is the preferred object persistence technology in iOS.) This way, when you want to save a new object, you just add that new object, and don't archive the whole collection of objects every time.
Furthermore, if speed is of primary interest and if your images are large, SQLite (the database that Core Data employs by default) is inefficient when handling large BLOBs (i.e. things like images). So, as inelegant as it sounds, you probably want to save images to your Documents folder, and only store a image file URL or path in CoreData.
why don't you save the image only on the init method ? if you create the object chances are you want to save it. so place the flag hasChanges == off in the init method and you check that flag for saving...
I am planning on creating my app in a 'Model-View-Controller'(MVC)-style, and in the end, for me at least, this means that all data is stored in the controller-class. Let's say I have a class Player, and the player has several objects of class Weapons or Equipment or whatever. The initialization of Controller* stores the player(s), so if I can store/save only the Controller-object over time, even if the app or the device restarts, that would be nice. I did this in Java one, I put in Serialization = 100L;(or something like it) in the top of the file of every object that would be included when saving the Controller-object, and it worked perfectly. Is this possible in ios/cocoa-touch/objective-c?
I have read and used Core Data (not very much), but that is just a database-table, sql?, which would have me extract every piece of information of every object?
For instance, if the object Player* has a member NSString *name;, I would have to save the actual string in Core Data, instead of saving the object of the player? Like, varchar.
If there is any way to store an entire custom object on the device for further use, I would very much like to know what it's called, and where I can read about it/tutorials.
Read up on the NSCoding protocol. You can make your object complient to it, then serialized it and save it to a file. Later you can restore it to the same state by using a decoder. For sure some other posts that cover this topic on SO.